Chromosomal abnormalities occur when chromosomes are either numerically or structurally abnormal, resulting in genetic diseases.
A person typically has 46 chromosomes/23 pairs of chromosomes, however, sometimes during embryo development a chromosome can be either gained or lost. For example, Down syndrome is a result of having one extra chromosome (47 instead of 46), and Turner’s syndrome is a result of having one less chromosome (45 instead of 46).
Structural chromosomal abnormalities occur when chromosomes are missing a part, have an extra part, or have switched places with another chromosome’s part. Structural abnormalities lead to either too much or too little chromosome material, which results in diseases such as Pallister Killian syndrome, and Cri du Chat syndrome.
Two Types of Genetic Testing Methods
1) Pre-implantation genetic diagnosis (PGD) is when an embryo is biopsied for the most common genetic conditions. This method is typically used when a wife, husband, or both may have a known genetic condition, a family history of a genetic condition, or may have a previous child with a genetic condition.
2) Pre-implantation genetic screening (PGS) / Next Generation Sequencing (NGS) is when an embryo is biopsied to determine the number of chromosomes it has. This method is typically used when a husband/wife have known infertility causes, previous miscarriages, and/or are older in age.
Testing for genetic diseases is used in conjunction with in‐vitro fertilization (IVF) to test embryos for chromosomal abnormalities prior to transfer. Some causes of infertility (recurrent abortion, etc) can be due to genetic abnormalities within the embryo. Therefore, testing the embryo for genetic abnormalities is a very important step to a successful IVF/ICSI cycle, and a healthy baby.
How it is performed?
In both PGS and PGD, one or more cells from the embryo are removed/biopsied on the 3rd or 5th day after fertilization and sent to an advanced genetic laboratory. The laboratory performs the respective genetic tests and sends us the detailed report. The doctor and embryologist will review the report, counsel the patient based on the report findings, and make the best plan to achieve the best outcome.